Have you noticed that indexed PDFs don't seem to contain all the content they should? Turns out this is a performance setting in Solr. The tip below is credit Uday Ogra of Adobe:

Solr has a default upper limit of 10000 on max number of words which can be indexed in documents which approximately defaults to 20-40 pages.

We can change this default value for each collection. Suppose collection's name is newcollection.

Open file COLDFUSION_COLLECTIONS_PATH/newcollection/conf/solrconfig.xml

Here COLDFUSION_COLLECTIONS_PATH is the path you would have configured while creating the collection.

Here search <mainindex> tag. Inside this tag there would be a sub-tag <maxFieldLength> which has a default value of 10000.

You can change it to a value which will suit your indexing.

(There is one more <maxFieldLength> tag directly under <indexDefaults> tag, do not change it)

In your case I would recommend to change it to 100000.

By the way on an average a single pdf page has around 200-500 words. So for a pdf with 100 pages setting this value to 100000 should be safe enough.